Technical considerations for saving lives
Clean water is an engineering problem and a community problem at the same time. Our technical team works out the science, and each local partner knows what their community will actually use. We iterate between the two, often five times over, until a solution is scientifically sound, wanted by the community, and built to last. This is where we show that work.
We don’t just apply academic science and engineering. We add systems thinking and economics, and we design closely with local NGOs so every solution is practical. That means iterating with the community, and usually starting with a pilot, until it works in the real world.
However deep you want to go, there’s a path
See what we do and where: the map, the projects, and the people behind them.
Explore our work →See what each solution really costs per person per year, and judge the impact-per-dollar yourself.
See the economics →Compare every solution by problem, read the technical briefs, or request one directly.
Compare solutions →What does clean water actually cost?
We track impact-per-dollar closely. Here’s the approximate cost to give one person safe water for a year: the initial delivered cost spread over each system’s expected life. Routine upkeep, paid locally, is not included. Judge for yourself.
Swipe the table sideways to see every column →
| Solution | Location | Cost (estimate) | People served | Expected life | $ / person / yr | Est. cost per life saved |
|---|---|---|---|---|---|---|
| Shared gravity membrane filter | DR Congo (Goma) | ~$80 per filter, all-in | ~25 (5 households) | ~5 years | ~$0.64 | ~$1,000 |
| Pipelines + filtration at the taps | Papua New Guinea | ~$25,000 for the full plan | ~8,500 | ~10 years | ~$0.30 | ~$450 |
| School ultrafiltration system | Cambodia (Kampot) | ~$700 per school | ~200–300 students | ~10 years | ~$0.25–0.35 | ~$500 |
| Ultrafiltration + UV village system | Philippines (Mariveles) | $533 | ~100–200 a day | ~5 years | ~$0.55–1.05 | Not estimated |
| Household biosand filter | Cambodia (Siem Reap) | ~$100 | ~7–20 | 10+ years | ~$0.50–1.40 | Not estimated |
$ per person per year is the initial delivered cost of each system spread over its expected life and the people it serves. Routine upkeep is paid locally and is not included. DR Congo: $80 per filter covers the filter, delivery, installation, training and materials. Papua New Guinea: about $5,000 for filtration on the existing line (3,500+ people whose water is untreated today), about $5,000 to extend the pipeline to about 1,500 more people, and about $15,000 for a new pipeline for about 3,500 more people. These are estimates; filtration and construction costs vary and depend on things we don’t know yet. Cambodia: the range reflects 200 to 300 students per school.
How we estimate cost per life saved
This is an estimate, not a measured result. We use it only for DR Congo, Papua New Guinea and Cambodia, where the people we serve have no safe water source today.
- People without safe water. About 703 million people lack even a basic drinking water service: 292 million walk more than 30 minutes to an improved source, 296 million drink from unprotected wells and springs, and 115 million drink untreated surface water (WHO and UNICEF, 2022 data). We use this group, not the 2.2 billion who lack safely managed water, because that larger number includes many people who already have a protected source nearby.
- Deaths from unsafe drinking water. Contaminated drinking water causes about 505,000 diarrheal deaths a year (WHO). A minority of those deaths happen among people who do have a basic service, so we count about 450,000 for the group above.
- People per death. 703 million ÷ 450,000 ≈ 1,560. We round down to about one death a year for every 1,500 people without safe water.
- Cost per life saved = cost per person per year × 1,500. DR Congo: $0.64 × 1,500 ≈ $1,000. Papua New Guinea: $0.30 × 1,500 ≈ $450. Cambodia: $0.35 × 1,500 ≈ $500 (using the lower count of 200 students per school).
How to read it. The estimate assumes people drink the treated water every day. If a household uses it only part of the time, the cost per life saved goes up. In DR Congo it is conservative: conflict, hunger and other illness raise death rates in Goma well above the global average, so fewer than 1,500 people are likely needed to prevent one death. In rural Papua New Guinea and Cambodia, where poverty is the main risk and there is no war or major epidemic, it is a reasonable middle estimate. A school system protects students during the school day, so the Cambodia figure is a rough guide. Sources: WHO drinking-water fact sheet; WHO/UNICEF Joint Monitoring Programme. Browse every project →
Solutions by problem
Every major solution, not just the ones we use, for the two water problems we work on. The right tool depends entirely on the water.
Swipe the table sideways to see every column →
| Solution | How it works | Best for | Targets | Approx. cost | Maintenance / life | Key tradeoff |
|---|---|---|---|---|---|---|
| Boiling | Heat to a rolling boil (1 min; 3 at altitude). | Emergency stopgap | Bacteria, viruses, protozoa | ~$75+/person/yr in fuel | None; not durable | Fuel & smoke; no residual |
| Chlorination | Free chlorine disinfects and leaves a residual. | Stored/piped water with a supply chain | Bacteria (6-log), virus (4-log); weak on Crypto | ~$0.66/person/yr; a $1.50 bleach bottle treats ~20,000 gal | Dosing checks; gear 5–10 yr | Taste; fails in turbid water |
| SODIS (solar) | Clear PET bottles in the sun 6 h (2 days if cloudy). | High-sun regions, small volumes | Bacteria, protozoa; weaker on virus | ~$0.30/person/yr | Swap bottles every 6–12 mo | Weather-dependent; ≤2 L |
| Ceramic filters | Water percolates fired clay (often silver-lined). | Household, locally made | 99% bacteria, >99% protozoa; limited virus | ~$3–7/person/yr ($15–50/unit) | Scrub; replace 2–5 yr | Slow flow; breakable |
| Biosand / slow sand | A living bio-layer plus sand traps & digests pathogens. | Durable household/community use | >98% bacteria, >99% protozoa, 85–90% virus | ~$100/unit; ~$0.26–4/person/yr | 10+ yr; swirl-and-dump top sand | Heavy; ~4-week ripening period |
| Hollow-fiber UF (Sawyer) | Gravity 0.1µm membrane; no power. | Dispersed households (our DRC default) | Bacteria (7-log), protozoa (6-log); limited virus | <$0.40 per 1,000 gal; ~$0.11–1.46/person/yr | Syringe backflush; 100,000+ gal life | Won’t remove viruses or chemicals |
| Powered / community UF | Pressurized hollow-fiber at kiosk or school scale. | With power + operator (our PH UF+UV) | Bacteria, protozoa; viruses only with a validated ~0.01µm membrane | ~$700 school unit (200–300 students); ~$0.25–0.35/person/yr | Membrane 5–15 yr; needs power | Capital cost + skilled upkeep |
| Reverse osmosis | High-pressure membrane rejects salts & metals. | Only when dissolved contaminants demand it | Salts, arsenic, fluoride, viruses | High capex + energy/opex | Membranes; pre-treatment | Wastes water; strips minerals; costly |
| UV disinfection | A UV-C lamp damages microbial DNA. | Clear water + power, point-of-entry | Bacteria, viruses, protozoa | ~$7–69/person/yr | Unit 5–10 yr; lamp replaced every 1–3 years depending on the model; clean the sleeve | Needs power; no residual |
| Coagulation / flocculation | Alum or PAC clumps fine particles to settle out. | Pre-treating turbid surface water | Turbidity; some pathogens & arsenic | Low chemical cost | Dosing & sludge removal | A pre-treatment, not disinfection |
| Rainwater harvesting | Roof catchment + first-flush + storage (a source). | High-rainfall regions | Low-contaminant source water | $2,000–5,000 (storage is >60% of cost) | Clean gutters/tank; 10–20 yr | Seasonal; storage dominates cost |
| Protected wells / boreholes | A sealed wellhead & apron (a source). | Areas with good groundwater | Reduces fecal ingress | Shallow $500–2,000; borehole $15k–40k | Pump upkeep; apron repair | May carry geogenic arsenic/fluoride |
| Arsenic removal | Iron-based adsorption (SONO), coag-filtration, or RO. | Arsenic groundwater (WHO 10µg/L) | Arsenic (III & V) | Iron is cheap; a SONO filter ran 15 yr at 600 ppb | Replace the iron matrix | Needs pH 6–7; As(III) needs oxidation |
| Fluoride removal | Bone char, activated alumina, or the Nalgonda technique. | High-fluoride belts (WHO 1.5 mg/L) | Fluoride | Media + regeneration cost | Periodic media swap | Capacity limits; safe disposal |
Our field principle: low cost protects more people. 99% safe water for 1,000 beats 100% safe water for 50. Pathogens are the default threat (match a filter, chlorine, or UV to a water test); arsenic and fluoride need contaminant-specific media or RO. Figures are approximate, from CWH field assessments cross-checked with WHO, US EPA, and CAWST.
Swipe the table sideways to see every column →
| Solution | How it works | Best for | Targets | Approx. cost | Maintenance / life | Key tradeoff |
|---|---|---|---|---|---|---|
| Activated carbon / biochar | Porous carbon adsorbs mercury (and cyanide); biochar is community-makeable. | Mercury in drinking water | Mercury, cyanide | Low; can be produced locally | Replace spent media | Methylmercury biomagnifies (the real danger) |
| Bone char | Hydroxyapatite chemically binds lead & cadmium (also fluoride). | Lead/cadmium in drinking water | Lead, cadmium, fluoride | Cheap; burn bone locally | Replace when saturated | Finite capacity; safe disposal |
| Iron-based adsorption | Iron hydroxides bind arsenic (and some Pb/Cd). | Arsenic-laden water | Arsenic | Iron is cheap and abundant | Replace media | Needs pH ~6–7 |
| Raise pH (dolomite / limestone) | Carbonate raises pH so metals precipitate; adds Ca/Mg. | Acidic, metal-rich water | Zinc & general metals; acidity | Locally abundant (e.g. Ghana) | Replenish media | Only partial for Pb/Cd/Hg |
| Ca/Mg ‘safening agent’ | Dietary calcium/magnesium displaces toxic metals in the body. | Reducing harm at a given exposure | Lowers metal toxicity | Cheap mineral pellets | Slow-dissolving | Mitigates harm; doesn’t remove metal |
| Mercury retorts (source) | Condense & recapture mercury vapor when burning amalgam. | Artisanal gold miners | Reduces mercury released | Cheap per device | Adoption-dependent | Occupational protection only |
| Gravity-borax (source) | Borax + gravity capture gold without any mercury. | Artisanal & small-scale mining | Eliminates mercury use | Cheaper; recovers more gold | Training | Needs local leadership / enforcement |
| AMD neutralization + wetlands | Limestone raises pH; constructed wetlands passively treat. | Acid mine drainage (pH 2.5–4) | Acidity, dissolved metals | Low opex; wetlands need land | Manage metal sludge | Generates sludge to dispose of |
| Cyanide degradation / green chem | Natural degradation, or replace cyanide leaching entirely. | Gold extraction (our Baguio R&D) | Cyanide | R&D-stage | Process change | Substitute still being proven |
| Phytoremediation | Hyperaccumulator plants pull metals into harvestable biomass. | Soils & sediments, slow cleanup | Metals (slowly) | Low cost | Harvest & dispose safely | Slow; don’t route biomass into feed |
| Modified SONO filter (our design) | One community-built unit: sand+iron+charcoal (As, Hg) + dolomite (pH, Ca/Mg) + bone char (Pb/Cd) + biochar (Hg, CN). | Multi-metal mining pollution | Arsenic, mercury, lead, cadmium, zinc | Mostly local materials | Needs before/after testing + lifespan est. | A CWH integrated design, in development |
Toxicity roughly follows mercury > arsenic > lead > cadmium > zinc, and acidic mine water makes every metal more soluble. Best solved at the source (mercury-free mining, AMD neutralization) and backstopped with selective adsorption media, which our Modified SONO filter combines into one community-built unit. Spent media and metal sludge must be disposed of safely.
Technical briefs
Full write-ups on the solutions we know best: the chemistry, the design choices, and the numbers. We’re publishing these one at a time.
How hollow-fiber UF and living biosand layers stop cholera & typhoid with no power or chemicals, and exactly where each one falls short.
Read the brief →UF is the core filter, but the right build depends on the water and the community. Prefilters, chlorine cleaning, UV, and activated carbon, and exactly when each one is worth adding.
Read the brief →Removing the two most toxic chemicals from artisanal gold without cutting the income communities depend on: mercury via borax and retorts, and cyanide via a thiosulfate substitute (our Baguio research).
Read the brief →Managing lead, cadmium, copper, and arsenic mobilized by gold mining, using pH adjustment and selective chemistry to keep metals out of water, soil, and food.
Read the brief →Why sponsoring one science or engineering student from a water-poor community ($1,500 a year) is the highest-leverage long-term water investment we make.
Read the brief →We publish our mistakes
Honesty about failure is how engineering improves, and how you know you can trust us.
During commissioning of our first Philippine village system, we broke a UV lamp. It cost time and money, and we rewrote our install checklist because of it. Every system since benefits from that mistake.
Across the sector, water systems given away entirely tend not to last, because people don’t value what they get for free. We now build in a small community contribution, which funds local operators and creates ownership.
In the DRC we deliberately avoided chlorine and complex builds. Gravity membrane filters remove the bacteria that cause cholera and typhoid without consumables or supply chains. The simplest design that solves the real problem wins.
A full field-notes blog is on the way. Subscribe below to get each new write-up.
External resources
We’re a learning center, and we don’t only point to our own work. When someone else explains it better, we link to them.
Start here
Drinking water
Want to go deeper?
Want a full technical brief, a techno-economic write-up, or a capacity statement for due diligence? Just ask, or lend your own expertise.